Real-time display systems based on spatial light modulators (SLMs) are increasingly being used as an alternative to display systems using cathode ray tubes (CRTs). SLM systems provide high resolution displays without the bulk and power consumption of a CRT system.
Digital micromirror devices (DMDs) are a type of SLM, and may be used in display applications. A DMD has an array of micro-mechanical pixel elements, each having a mirror and a memory cell. Each pixel element is individually addressable by electronic data. Depending on the state of its addressing signal, each mirror is tilted so that it either does or does not reflect light to the image plane, i.e., so that it is on or off. The proportion of time during each video frame that a mirror is in an on state determines shades of gray--from black for zero on time to white for 100 percent on time.
Existing DMD display systems are projection systems. Light from the on mirrors passes through a projection lens and creates images on a large screen. Light from the off mirrors is reflected away from the projection lens and trapped. Color may be added in two ways, by a color wheel or by a three-DMD configuration.
DMDs may be fabricated using semiconductor fabrication techniques. To fabricate a DMD, standard CMOS processing steps are completed for a static RAM, which comprises the memory cells, and for address electrodes. Then, a "roof" of tilting mirrors is fabricated over the memory and address circuit. The height of this superstructure is enough to allow the mirrors to tilt plus and minus 10 degrees or so about a torsion axis.
The display optics for viewing the image generated by the DMD is easily implemented for projection viewing. For example, the DMD may be coupled with dark-field projection optics. Here, a bright light source is directed to the chip at an angle to its surface. Mirrors tilted to an on position reflect the incoming light through a projection lens and onto a screen. Mirrors tilted to an off position reflect the incoming light so as to miss the projection lens.